1. Field of the Invention
The present invention relates to a valve device used in a control of circulation of an exhaust gas in exhaust gas recirculation (EGR) device, which recirculates a part of the exhaust gas from an engine of an automobile to an intake system to suppress generation of an inert gas for obtaining a good rate of fuel consumption, and so on, wherein the valve device is driven by a direct current brush motor.
2. Discussion of Background
FIG. 6 is a cross-sectional view illustrating a structure of such a valve device disclosed in, for example, Japanese Unexamined Patent Publication JP-A-10-21306.
In FIG. 6, numerical reference 1 designates a motor case; numerical reference 2 designates a rotor, accommodated in the motor case 1 and supported by a slide ball 3 at a top end thereof and by a ball bearing 4 at a bottom end thereof, and wound by a coil 5; and numerical reference 6 designates a stator located in an inner wall of the motor case 1 to surround the rotor 2 and having a permanent magnet magnetic pole 7 at a position corresponding to the coil 5 of the rotor 2.
Numerical reference 8 designates a commutator attached to an upper portion of the rotor 2; numerical reference 9 designates a brush, being in contact with the commutator 8 a pressure by the spring 10, for supplying a direct current supplied via a connector terminal 11 to the commutator 8; numerical reference 12 designates a valve case coaxially connected to the motor case 1; numerical reference 13 designates a motor shaft, screwed inside the rotor and being movable in an axial direction through a guide bush in response to a rotation of the motor; numerical reference 15 designates a valve driving shaft connected to a tip of the motor shaft and movable through the guide plate; numerical reference 17 designates a valve member, fixed to a tip of the valve driving shaft 15, for opening and closing a flow passage 19 by being in contact with a sealing member 18 located inside the valve case 12.
In thus constructed conventional valve device, when the direct current supplied through the connector terminal 11 is applied to the coil 5 of the rotor 2, a direct current motor is formed in corroboration with the permanent magnet magnetic pole 7 of the stator, whereby the rotor 2 is rotated. Along with the rotation, the motor shaft 13 screwed inside the rotor 2 is rotated, whereby the motor shaft 13 moves in response to an amount of the rotation, namely, it moves downward in FIG. 6. Therefore, the valve member 17 secured to a tip of the motor shaft 13 to be separated from the sealing member 18, whereby the flow passage 19 is released.
However, because thus constructed conventional valve device opens and closes the flow passage 19 by contacting and separating the valve member 17 and the sealing member 18 through the valve driving shaft 15 connected to the motor shaft, which is screwed inside the rotor 2 to be upward and downward moved by the rotation of the rotor 2, the motor shaft 13 should be inserted in and engaged with the rotor 2, and the coil 5 should be wound around an outer periphery of the rotor 2, whereby an outer diameter of the rotor 2 is increased. Therefore, there are problems that a moment of inertia is increased, and responsiveness of valve opening and closing operations is deteriorated.
It is an object of the present invention to solve the above-mentioned problems inherent in the conventional technique and to provide a valve device having excellent responsiveness of a valve opening and closing operation by reducing inertia of a rotor.
According to a first aspect of the present invention, there is provided a valve device comprising: a stator formed by arranging a predetermined number of coils in peripheral directions of a stator core with substantially equal intervals; a rotor formed by arranging a plurality of permanent magnet magnetic poles at positions respectively corresponding to the coils on an outer peripheral surface of the stator; a current carrying means commutating a direct current supplied from a power source through the rotor and applying this to each of the coils of the stator; a shaft member located in a center of the rotor and movable in a direction of the shaft in response to rotation of the rotor; and a valve member opened and closed by movement of the shaft member.
According to a second aspect of the present invention, there is provided a valve device according to the first aspect of the present invention, wherein the current carrying means includes: a commutator monolithically formed with the permanent magnet magnetic poles by a resin in the rotor and divided into many parts to commutate the direct current supplied from the power source through a first brush; and as much as n slip rings, electrically connected to corresponding divided parts of the commutator to apply a current commutated to n phases by the commutator through a second brush to corresponding coils of the stator.
According to a third aspect of the present invention, there is provided a valve device according to the second aspect of the present invention, wherein the commutator is formed by dividing a center or an outer peripheral annular portion of a disk into many parts in peripheral directions, and the slip ring is formed by dividing into n parts like concentric rings on an inner peripheral side or an outer peripheral side of the commutator.
According to a fourth aspect of the present invention, there is provided a valve device according to the first aspect or the second aspect of the present invention, wherein the current carrying means and the valve member are positioned different sides of the stator and the rotor in the direction of the shaft.
According to a fifth aspect of the present invention, there is provided a valve device according to the first aspect of the present invention, wherein the stator is formed by winding coils respectively around magnetic pole teeth of the stator core, formed by laminating a magnetic material and connecting a plurality of yokes like a belt, and bending the connecting portions to be in an annular shape.